With recent advances in optical technologies, most notably wavelength division multiplexed (WDM) transmissions, the amount of raw bandwidth available on fiber optic links has increased by several orders of magnitude. Meanwhile, the ubiquity of the Internet Protocol (IP) has led to the much-touted IP-over-WDM as the core architecture for the next generation Optical Internet. This is due mostly to the expectation that such an architecture will streamline both network hardware and related software, and at the same time, result in a flexible and even future-proof infrastructure with virtually unlimited bandwidth. Undoubtedly, harnessing the bandwidth to effectively support IP and other high-layer protocols such as ATM in an efficient and scalable manner is vital to the continued growth of emergent optical networks.
There have been a number of proposed solutions to this problem. These include:
Wavelength Routing, which involves quasi-statically or dynamically establishing wavelength paths (circuits) for IP traffic; Multi-Protocol Lambda Switching, which extends the control framework of Multi-Protocol Label Switching (MPLS) to wavelength routing by treating each wavelength as a label; Optical Packet Switching: which utilizes the same concept as traditional packet switching, but the payload (data) is kept in the optical domain by using fiber-delay lines (FDL), while the packet header (control info) is processed either optically or converted back to an electronic signal then processed; Optical Label/Tag Switching, which uses a fixed length payload with a header containing a label/tag carried by sub-carrier multiplexing; and Terabit Burst Switching, in which variable length bursts (packets) are sent on a separate wavelength and set-up packets are electronically processed to make open-ended reservation (using explicit release or refresh packets). No offset time (or only an insignificant one) is used between a setup packet and its corresponding burst, which must be delayed using FDLs at intermediate nodes. Generalized MPLS or G-MPLS further extends MPLS to TDM (SONET) networks, but can only apply to wavelength-routed networks, TDM networks and electronic packet networks, not optical burst switched (OBS) networks.
These prior solutions all fall short in some way. Wavelength-Routing and Multi-Protocol Lambda Switching are not scalable as the number of wavelength paths that can be established is limited. They are also inefficient as the IP traffic is “bursty”. Further, traffic aggregation/grooming at the edge, and reconfiguration of wavelength paths are complex. Optical packet-switching, Optical Label switching and Terabit Burst Switching methods all require FDLs, which are bulky and can only provide limited delay, and are uneconomic to implement.
Recently, optical burst switching (OBS) has been proposed as another solution to the problem of harnessing the bandwidth. OBS uses an optical switching paradigm to combine the best features of optical circuit switching and packet/cell switching. It provides improvements over Wavelength-Routing in terms of bandwidth efficiency and core scalability via the statistical multiplexing of bursts. In addition, by sending a control packet carrying routing information on a separate control wavelength (channel) with an offset time, i.e., a lead time before the transmission of the corresponding burst (or data), the use of FDLs can be eliminated. The OBS and its operation, as discussed in detail in C. Qiao and M. Yoo, “Optical Burst Switching (OBS)—A New Paradigm For An Optical Internet,” Journal of High Speed Networks, 1999, Volume 8, Number 1, pp. 69-84, is hereby incorporated by reference as if fully set forth herein.
Furthermore, when compared to Optical Packet Switching where each packet has a fixed length and contains a header, OBS incurs a lower control (and processing) overhead as the length of a burst can be variable, and on average longer than that of a packet. In addition, under OBS a control packet and its corresponding burst can be much more loosely coupled in both space (by using separate control and data wavelengths) and in time (by using a nonzero offset time) than a header and its payload are in Optical Packet Switching, and hence, the requirements on processing control packets, and on synchronizing between bursts (as well as between a burst and its control packet) in OBS can be much less stringent than those on processing packet headers, and on synchronizing between packets (as well as between a packet's payload and its header) in optical packet switching.
Although OBS is a better solution than Wavelength-Routing, Multi-Protocol Lambda Protocol and Optical Packet Switching, it still requires a separate WDM layer (or so-called optical cloud) with separate mechanisms for addressing, routing, resource provisioning and so on. The advantage of integrating IP-over-WDM, as opposed to having an IP layer as well as a separate WDM layer, is that the integrated solution can reduce redundancies in software and hardware, increase efficiency, facilitate traffic engineering and network survivability, multi-vendor interoperability, interworking between heterogeneous networks, as well as having the potential for migration to optical packet-switched networks in the future.
It is, therefore, an object of the current invention to provide an integrated IP-over-WDM network solution to achieve the above advantages. It is a further object of the invention to achieve better bandwidth utilization when compared to previous optical circuit switching methods such as Wavelength Routing where wavelength paths are established using a two way process, by allowing for statistical sharing of each wavelength among flows of bursts that may otherwise consume several wavelengths. One further object is for the invention to support all optical data communications without requiring optical memory devices such as fiber delay lines, and offer interoperability with other MPLS-enabled networks.